1. Technical Field
The invention relates to apparatus and methods for detecting telephone-activated devices, such as cell telephones, in an idle state or mode.
2. Description of the Related Art
Telephone-activated devices, such as cell telephones, pagers, beepers, etc., have greatly multiplied over the past several years. This has been a boon to users, allowing people to be reachable by telephone, even at times and in places where they are not otherwise reachable at a fixed telephone number. However, this blessing has been a mixed one, in that increasingly, telephone-activated devices intrude into places where ringing tones and/or telephone conversations are unwelcome, such as in theatres, restaurants, and public transportation. In addition, safety concerns have been raised regarding the location of telephone-activated devices in certain situations, for example, in hospitals, aboard aircraft, or within proximity to gasoline pumps used to refuel vehicles. Accordingly, in recent years systems have been put into place to prevent use of cellular telephones in certain designated areas.
One type of system involves area-based detecting a cellular telephone in its idle state, in a certain fixed region such as entryway doorway or room. One example of such an apparatus is described in U.S. Pat. No. 6,490,455, titled “Apparatus and Method for Detecting a Mobile telephone in Idle State.” Such a device involves detecting mobile telephones in a fixed detection area, and providing an alarm to an operator when a mobile telephone in a passive or idle state is detected. Such systems are limited to providing coverage in a fixed detection area. Another drawback to such systems is that they provide mere notification only, and do not themselves take any action to prevent mobile telephones from receiving incoming calls.
Another approach is to provide an array of wires along the perimeter of a sensitive area, thereby blocking signals from cellular telephone towers or base stations from entering into the sensitive area to activate any idle-state mobile telephone within the area. An example of this sort of system is described in U.S. Pat. No. 6,222,654, which discloses such a system being located along the perimeter of a gasoline station. As with the area-based detection system described above, the blocking system only operates over a fixed area, and does not prevent cellular telephones from receiving incoming calls outside of the perimeter of the designated area.
One problem that has arisen from the proliferation of inexpensive cellular telephones and other telephone-activated devices is use of such devices to remotely trigger explosive devices. Cellular telephones are inexpensive to obtain, and may be difficult to trace. The battery of a cellular telephone in a passive idle state may last several days, allowing an explosive with a cell-phone trigger to be placed in luggage, cargo, or other locations. Telephone calls over long distances, even over international networks, may be used to detonate such devices. Further, detection of cell pones in the idle state is difficult, because transmissions from cell telephones while in an idle state are short and infrequent, for example, on the order of tens of minutes.
The above-described area-oriented methods of detecting or impeding operation of cellular telephones are ill-suited for detection of telephone-activated devices used as triggers for explosive devices. This is because the above area-oriented systems require use of a dedicated area in which cellular telephones are detected or prevented from operating. Systems which merely prevent cellular telephones from receiving incoming calls in the designated area provide very limited protection, since they do not prevent cellular telephones from receiving incoming calls once they leave the designated area. Systems that provide detection in the designated area may not prevent the receipt of incoming calls in the designated area, and in addition require objects which may contain cellular telephones or other telephone-activated devices to be brought into the designated area. The latter limitation may be significant in situations where objects which may contain a cellular telephone trigger may be spread over a large region, for example, when unloading shipping containers that may have an object containing a cellular telephone in an idle state. Use of such systems over a large area may be prohibitively expensive.
From the foregoing, it will be appreciated that improvements in telephone-activated device detection systems and methods would be desirable.